1. Field of the Invention
The present invention relates to an object, a method, or a fabrication method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a driving method thereof, or a fabrication method thereof. In particular, one embodiment of the present invention relates to a heterocyclic compound and a novel method of synthesizing the same. In addition, one embodiment of the present invention relates to a light-emitting element, a light-emitting device, an electronic appliance, and a lighting device that include the heterocyclic compound.
2. Description of the Related Art
A light-emitting element using an organic compound as a luminous body, which has features such as thinness, lightness, high-speed response, and DC drive at low voltage, is expected to be used in a next-generation flat panel display. In particular, a display device in which light-emitting elements are arranged in matrix is considered to have advantages in a wide viewing angle and excellent visibility over a conventional liquid crystal display device.
The light emission mechanism is said to be as follows: when a voltage is applied between a pair of electrodes with an EL layer including a luminous body provided therebetween, electrons injected from the cathode and holes injected from the anode recombine in the light emission center of the EL layer to form molecular excitons, and energy is released and light is emitted when the molecular excitons return to the ground state. Singlet excitation and triplet excitation are known as excited states, and it is thought that light emission can be achieved through either of the excited states.
An organic compound is mainly used for an EL layer in such a light-emitting element and greatly affects an improvement in the characteristics of the light-emitting element. For this reason, a variety of novel organic compounds have been developed (e.g., Patent Document 1).